1. Field of the Invention
This invention relates to medical instruments and, in particular, to a cannula valve and seal system for use with an instrument such as a trocar.
2. Description of Related Art
During the performance of laparoscopic surgery, it is not uncommon to use as many as five trocars in a single procedure in order to advance operating instruments into the abdominal cavity of a patient. The valving system employed with the cannula that holds and guides the trocar is very important. First, the valving system must prevent the loss of insufflation gas leaking out of the abdominal cavity whether or not instruments are present within the cannula lumen. Second, the valving system must pose little or no resistance to the advancing of instruments or the withdrawal of tissues through the valving system. Third, given the fact that many different trocars of varying outside diameters are available for use and because space is limited around the operating table, it is desirable that the trocars be operatable using just one hand. In particular, it is desirable that only one hand be necessary to advance the instrument into the patient and to withdraw the instrument with tissues on it without stripping the tissues off or causing the tissues to hang up in the valve and seal system.
In the prior art, it was common to seal off gas leaks by using a two-component valve employing a gasket/seal arrangement. The first valve is typically located in the cannula housing and seals when the trocar or other instrument is not present. A second gasket/seal, which is removable and exchangeable and sized for instruments of varying diameters, is located proximally with respect to the first seal thereby sealing the cannula as the trocar is introduced into it or removed from it. One of the major problems with such prior art systems is that they require two hands for operation and do not satisfactorily seal the cannula from the loss of insufflation gas.
For example, U.S. Pat. Nos. 4,654,030; 4,931,042; and 5,030,206, describe a swinger flapper valve that swings closed when instruments are not present and a gasket/seal located proximally to the valve to seal the lumen when instruments are present.
U.S. Pat. Nos. 4,535,773 and 4,972,827 describe a trumpet type valve or slide valve which is spring-loaded to close the lumen when instruments are not present and includes a gasket/seal similarly located proximally to seal the lumen when instruments are present. These devices and others currently known in the prior art typically require a manual movement and the use of two hands to open and close the valve. Additionally, this prior art is mechanically more complicated, and thereby more costly and more difficult to clean when re-sterilization and reuse are intended. They do not provide for the easy passage of irregularly shaped instruments, and most importantly, are not adapted for the easy passage of tissue. Further, the changing of seal/gaskets is cumbersome, and because they are separate components, they become loose making them difficult to account for during use.
There have been several attempts to solve such problems in the prior art. Several devices use commercial duckbill-type check valves such as described in U.S. Pat. No. 5,010,925 and similar to those commonly used in automotive, appliance, medical and specialty applications. Such prior art duckbill valves are slit at one end to create one set of converging lips. While these prior art valves are effective for liquids and gases, they are not effective for use in laparoscopic surgical procedures because they do not allow for the easy withdrawal of tissues. Sample tissue is easily dislodged from devices grasping them as strong resistance from the valve is encountered during the withdrawal process. Occasionally, the resistance is large enough to cause the unintended withdrawal of the cannula from the patient's abdominal cavity.
U.S. Pat. No. 4,960,412 describes the application of a duckbill valve having a concave design but differing from other prior art designs in that bosses on the valve acting on inner surfaces of the valve holding chamber, rather than gas pressure, keep the valve closed. This type of valve would be particularly adverse to passing tissue in the opposite direction because the opposing bosses, designed for the purpose of maintaining closure of the lips by blood pressure, is contrary to the concept of allowing easy passage of tissues or irregularly shaped instruments that can "hang up" or "catch on" the valve and be difficult to remove.
U.S. Pat. No. 5,122,122 describes a duckbill valve having a spherical design. The lips have a deliberately thin design, which causes them to fold back on themselves, thereby turning inside out. They exhibit unacceptably high withdrawal resistance and further are not able to adequately seal. Additionally, due to the delicate nature of the lip edge, the valves are easily damaged by tears and/or cuts made by sharp instruments passing through them. This wear ultimately makes the valve difficult to seal.
U.S. Pat. No. 5,242,412 describes a valve having converging sealing lips which generally operates according to the principles of commercially available duckbill valves such as described in U.S. Pat. No. 5,010,925. This includes internal converging walls and an associated slit which terminates at the apex of a "V". It creates one set of delicate valve lips which are easily damaged. Further, they are not conducive to passing tissues and instruments through without high forces of resistance. When all is considered, it exhibits the same disadvantages common with all the prior art designs. Further, by nature of the valve design, additional diverging lip extensions are needed to prevent the inward collapse of the sealing lips. It appears that the lip extensions could potentially interfere with consistent, reliable valve closure.
Finally, the prior art does not disclose valves which are easily removable and/or replaceable as required in reusable device applications.